How do GABA-B receptors on a terminal reduce the transmitter it releases? · Grey Matter

Presynaptic GABA-B receptors activate G proteins whose freed subunits bind the terminal's voltage-gated calcium channels and make them harder to open.

How do GABA-B receptors on a terminal reduce the transmitter it releases?

Presynaptic GABA-B receptors activate G proteins whose freed subunits bind the terminal's voltage-gated calcium channels and make them harder to open. Because release rises with roughly the fourth power of calcium entry, a modest cut in calcium lowers the probability of release substantially. On GABA terminals this is autoinhibition, limiting how much GABA the next spikes release; on glutamate terminals, as heteroreceptors, it lets nearby inhibition turn down excitation. Baclofen, a GABA-B agonist, uses this effect in the spinal cord to reduce spasticity.